The human immunodeficiency virus (HIV) has been unequivocally established as the etiologic agent of acquired immune deficiency syndrome (AIDS). The development of AIDS is typically associated with a decline in CD4+ helper T cells due to the tropism of the HIV envelope glycoprotein gp120 for CD4. However, long before the onset of clinical AIDS, multiple defects in T cell function are seen in patients with HIV infections. Binding of gp120 to its 'receptor' not only allows for viral entry into T lymphocytes, but also initiates a series of biochemical events that renders these cells hyporesponsive to antigen. Recent evidence suggests that CD4 ligation activates a number of kinases, including protein kinase C and receptor-associated tyrosine kinases. In view of the defined role of protein phosphorylation in regulating the function of a variety of receptors, it is hypothesized that the binding of gp120 to CD4 leads to a kinase-mediated uncoupling of the T cell antigen receptor (alpha- beta TCR) complex from intracellular second messenger generating systems. This signaling defect may indeed account for the progressive impairment of immune responses to both the human immunodeficiency virus and other pathogens that is characteristic of AIDS. Two related lines of investigation will be pursued to define the molecular basis of gp120-induced T cell hyporesponsiveness. In Aim 1, the molecular site of action of CD4-mediated disruption of alpha-beta TCR signaling will be investigated in a number of T cell models. The molecular basis of signal transduction following alpha-beta TCR ligation is known to involve a cascade of early and late events that can readily be measured. Using assays of calcium mobilization, protein phosphorylation, and polyphosphoinositide metabolism in conjunction with various specific inhibitors, the molecular site of uncoupling will be localized. Later events, such as IL2 receptor expression, IL2 secretion, and proliferation will also be analyzed. Aim 2 will attempt to define the contribution of protein kinase activation following CD4 ligation to the uncoupling of alpha-beta TCR-mediated signal transduction. This will be accomplished by using assays of specific kinases in conjunction with inhibitors and assays of signal transduction noted above. Additionally, immunoprecepitation of various kinases will be carried out and their activity and specificity will be assessed using both in vivo and in vitro assays.